The present invention relates to an improvement in yarn cabling machines and more particularly in machines used for cabling glass yarns, namely machines producing very long textile elements resulting from the twisting together of at least two strands.
The invention relates more particularly to an improvement made in the machines such as described in French Pat. No. 1 208 273.
More generally, the aforesaid French Patent describes, as diagrammatically illustrated in accompanying FIG. 1, a cabling machine in which every working position comprises an assembly similar to unwinding double twist spindles (or DT assembly) permitting to twist together the two strands (A-B) supplied from two supply sources (1) and (2). In the device, the feeding bobbins (1) and (2) supplying the two strands (A) and (B) are placed one below the other. The yarn (A) supplied from bobbin (1) goes through a similar rotary plate (3) so as to form a balloon (4) inside which is situated the feeding source (2) supplying the strand (B). Strands (A) and (B) are twisted together at their meeting point (5) and the formed cabled yarn (6) is wound in conventional manner, for example by a throwing type winding (7).
The supply of the two strands (A) and (B) constituting the cabled yarn (6) is initiated by the winding speed in (7) and tensioning devices (8,9) are provided for each of said strands (A) and (B) in order to equalize the tensions and to obtain a balanced assembly.
The system used to assemble the two strands at meeting point (5) essentially comprises, as illustrated in FIGS. 1, 2 and 3 of the aforecited patent, a rotary "ply head", mainly constituted by a U-shaped support comprising two parallel branches of different length. This support is mounted on a ball bearing and is rotatable. Grooved pulleys are mounted on said support for guiding the yarns, the two strands being twisted together downstream. The support is driven in rotation directly by the balloon of the strand passing through an opening provided in the longest lower branch.
This type of machine is on the whole satisfactory although it has been found, especially in the case of glass yarns, that the variations of tension which are liable to occur when winding the cabled yarn could cause irregularities and even breakages in said yarn.
In addition, the system which is used to join the two strands is complex and is liable to continue working even if one of the strands, constituting the cabled yarn, breaks.
It has now been found, and this is the object of the present invention, to improve the cabling machines of the aforementioned type in such a way as to overcome the aforesaid disadvantages and in particular to obtain a regular and constant tension on the strands, as well as to stop automatically the machine if one of the strands constituting the cabled yarn should break.
In general, the cabling machine according to the invention differs from that described in the aforementioned French Patent, in that:
on the one hand, the two strands of yarn are twisted on a roller mounted for free rotation and situated in the axis of the upper bobbin, the strands being in contact with part of the peripheral surface of said guide and,
on the other hand, the twisted strands are subjected, after their passage over the joining guide and before winding, to the action of a compensating system which can absorb the variations of tension and can actuate means of controlling the stoppage of the machine if one of the strands constituting the cabled yarn, breaks.
According to a preferred embodiment of the invention, the tension compensating system is constituted by a lever arm mounted for pivoting on the frame of the machine, the arm comprising at its free end, a yarn-guiding wheel, which, in normal operation, is disposed so that the resulting cabled yarn travels up the rotary doubling guide over about a quarter of its periphery, said arm being subjected to the action of a return spring (or like member), so that it is freely pivotable between two limit positions on either side of a balancing point, positions beyond which it can actuate the means controlling the stoppage of the machine.